1. Field of the Invention
The invention relates in general to a method of fabricating an integrated circuit. More particularly, this invention relates to a method of fabricating an interconnection structure of a capacitor.
2. Description of the Related Art
The capacitor and inductor are the major devices in the oscillation circuit of a radio frequency (RF) device. A capacitor in the oscillation circuit is typically in a metal-insulator-metal (MIM) stack structure. That is, the capacitor includes a bottom metal electrode plate, an inter-metal dielectric layer (IMD) and a top metal electrode plate. The bottom metal electrode plate is electrically connected to the substrate, and the top metal electrode plate is electrically connected to another metal layer. The method for fabricating a such conventional capacitor is described as follows.
In FIG. 1A, a substrate 100 having a capacitor 110 that has been formed thereon is provided. The capacitor 110 comprises a bottom metal electrode plate 112, an inter-metal dielectric layer 114 on the bottom metal electrode plate 112 and a top metal electrode plate 116 on the inter-metal dielectric layer 114. A dielectric layer 130 is formed to cover the substrate 100 and the top metal electrode plate 116.
In FIG. 1B, via holes 140 are formed within the dielectric layer 130 to expose a portion of the top metal electrode plate 116. The via holes 114 are then filled with metal material to form plugs 150, which completes the interconnect of the capacitor.
Using the conventional method described above, the quality factor (the Q-value) of the capacitor 110 is degraded. The reason is explained as follows. The Q value is equal to a ratio of the electric energy stored in the electrode plate to the energy consumption. The energy consumption is a sum of the energy consumed in the metal bottom electrode plate 112, the metal top electrode plate 116, the plugs 150 and the metal layer 160. Because the cross section of the plug is small, the resistance is great which increases energy consumption. In addition, a skin effect is caused during a high frequency operation, that is, a majority of current is converged on a portion of the surface of the plugs 150. The resistance of the capacitor is increased which results in higher energy consumption. Consequently, the Q value is decreased.
The invention provides a method of fabricating an interconnect of a capacitor. A substrate comprising a capacitor thereon is provided. The capacitor comprises a metal bottom electrode plate electrically connected to the substrate, an inter-metal dielectric layer on the metal bottom electrode plate and a metal top electrode plate on the inter-metal dielectric layer. A spin-on dielectric layer is formed to cover the metal top electrode plate of the capacitor and the substrate with a portion on the metal top electrode plate thicker than a portion on the substrate. The spin-on dielectric layer is etched back to expose a surface of the metal top electrode plate. A metal layer is formed on the spin-on dielectric layer and the metal top electrode plate to have a direct contact with the surface of the metal top electrode plate. The metal layer is then patterned to form an interconnect of the capacitor.
In the above method, if an inductor is formed on the substrate together with the capacitor, a surface of the inductor is also exposed after etching back the spin-on dielectric layer. The metal layer is thus formed in contact with not only the surface of the metal top electrode plate of the capacitor, but also the surface of the inductor. After being patterned, an interconnect of the inductor is also formed.
An interconnect of a capacitor is further provided by the invention. The interconnect comprises a metal layer formed on a dielectric layer and in contact with a metal top electrode plate of a capacitor. In addition to the top electrode plate, the capacitor further comprises a metal bottom electrode plate on a substrate and an inter-metal dielectric layer on the metal bottom electrode plate.
Thus formed, the interconnect of the capacitor is in direct contact with the metal top electrode plate, so that the resistance of the interconnect and the contact resistance between the interconnect and the capacitor is decreased to reduce the energy consumption. The Q factor can thus be enhanced effectively. In addition, when an inductor is formed on the same substrate on which the capacitor is formed, a direct contact between the interconnect and the inductor is also established to minimize the resistance, so that the Q factor of the inductor is also enhanced.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.